Inside the California Teachers Study: The Finding

March 2, 2017
| by Stephanie Smith

“News about breast cancer,” was the introduction from Monica Gayle, a "CBS Morning News" anchor, during a 1994 broadcast. “Young women can reduce their chance of getting the deadly disease with just a little exercise.”

Leslie Bernstein, early in her career

The segment went on to explain that women who exercised at least four hours a week during their reproductive years could reduce their breast cancer risk by 50 percent — and between one and three hours of physical activity a week reduced it 20 to 30 percent.

The gleam of the news media — on CBS, "Good Morning America," "The Today Show," and in most major newspapers across the country — was shining on a young biostatistician and cancer researcher named Leslie Bernstein, Ph.D., who, two years later, would help launch the California Teachers Study, a seminal study involving more than 133,000 teachers.

“When you work that hard and happen to be the national news of the day, it’s a big deal,” said Dennis Deapen, Dr.P.H., an epidemiologist and — at the time — a colleague of Bernstein’s at the University of Southern California. “Every woman watching that broadcast could ask herself that question, ‘Do I want to do something about this?’ And no doubt many did. That’s public health.”

This big news about breast cancer came at a time when the disease was still considered a death sentence.

“There had not been any good news, ever, on breast cancer,” said Bernstein during a recent interview in her office in the Division of Biomarkers of Early Detection and Prevention at City of Hope. “All we knew about then were things that increased your risk, and you couldn’t do a damn thing about them.”

These should have been heady times for a biostatistician, but upon reflection, 23 years later, Bernstein says she tempered her enthusiasm. What she remembers more than the media and public attention is a sort of agonizing process leading up to it — the churning in her mind — trying to disprove her own study’s finding.

“The frustration is what if I’m wrong?” said Bernstein. “I was trained that when you have something that’s so definitive, maybe there’s something missing and it’s not really true and you try to disprove it.

“We did the most complete statistical analysis that you could do, looking at every potential way to make the finding go away.”

But no matter how many ways Bernstein approached the data, the finding stuck.

Similar studies from researchers around the world confirmed her finding. “Now we have more than 60 studies all showing that women who exercise have a lower risk of breast cancer,” said Bernstein. “Not a guarantee, but they have lower risk.”

Dennis Deapen, Dr.P.H.

Around the time her study was published, Bernstein and two colleagues at USC — Ron Ross, M.D., an expert in hormones and cancer, and Deapen — were discussing doing a study of teachers. As it turned out, there were similar murmurings happening among other researchers in California.

None of these groups, however, had the funding needed to do the studies.

But things were happening behind the scenes legislatively that would make their musings about a teachers study real.

A group of breast cancer advocates had been working with a California state assemblywoman, Barbara Friedman, to fund more breast cancer research. From that advocacy sprung legislation — and a small, steady stream of funding for research that would come, oddly enough, from a tax on tobacco.

“It was interesting and kind of inexplicable since breast cancer has never been particularly strongly linked to tobacco,” said Deapen. Still, the feeling among advocates was there was not enough known about this deadly disease — and they wanted a better picture of why it developed.

“The breast cancer movement was really energized at the time,” said Michele Rakoff, executive director of the Breast Cancer Care and Research Fund, and a breast cancer survivor. “A lot of us took our lead from the AIDS activists, but we didn’t just want to ‘ACT UP.’ We were saying, ‘Breast cancer is an issue — women continue to get it — and we want to learn more about it.’”

Funds earmarked by the legislation went to the California Cancer Registry (CCR), a database that tracks cancer cases diagnosed statewide. But big questions remained: How would the study be structured? What group would be studied?

Researchers from around the state — including the regional leaders of the CCR, Bernstein and her colleagues at USC, researchers from University of California, Irvine and a group then called the Northern California Cancer Center — got together to decide.

It was a rare opportunity — the sort of thing that would make even the most stolid researcher giddy.

“It was the most fun I’ve ever had in my professional career,” said Deapen. “Engaging with these other people and just throwing around ideas and saying, ‘How can we really make this work?’”

Those lively scientific discussions were happening around the same time big findings about cancer, hormones and other diseases were emerging from the Harvard Nurses’ Health Study. More than one person involved in the meetings suggested a structure like the Harvard study — called prospective, because it involves collecting data, following people over time and linking life events with health outcomes in the future — but focused on California teachers.

Michele Rakoff, Breast Cancer Advocate

“Why teachers?” said Rakoff, a member of the steering committee for the California Teachers Study since its inception. “Teachers respond. Teachers are very interested in giving you information about themselves, and they are very interested in filling out surveys."

Above all, she added, “Teachers do their homework.”

But there was another big reason to choose teachers: They were more likely to get breast cancer.

“No one knew why they were at an increased risk,” said Bernstein. “So if you do a study, you might as well start with the people that you know have increased risk.”

Besides that, teachers in California smoked at dramatically lower rates than the state average. Overall rates of smoking among women were around 21 percent when the study started, according to the Centers for Disease Control and Prevention, while smoking rates among teachers hovered closer to 4 or 5 percent.

Lower smoking rates would remove a potentially huge confounder — a cumbersome extra step when analyzing the data of factoring in how smoking influenced cancer rates.

Teachers, it turned out, were a near-perfect study group.

The next and most challenging step after deciding on a teacher cohort was recruitment: How to reach out to hundreds of thousands of teachers?

“We didn’t know who the teachers were — that was not public information,” said Deapen, now the co-principal investigator of the California Teachers Study. “We couldn’t just call up the state and say, ‘Send me the names and addresses of all the teachers in California.’ They would say no.”

The group circumvented that challenge by working with the State Teachers Retirement System, or STRS, which had contact information for current and former teachers in California. With some convincing, STRS agreed to provide mailing labels for 400,000 introductory packets on behalf of the newly formed study.

Once the letters finally were mailed, “There was eager, eager anticipation, and uncertainty about what the response would be,” said Deapen.

The response was bigger than expected: More than 133,000 signed up, “Which is huge — huge,” said Deapen.

The California Teachers Study had gotten its start.

Stories of Hope is a monthly series that explores important issues in health care. This series is an inside look at the beginning, and future, of the California Teachers Study. Part 1 was a look at the statistician who would change how we view breast cancer risk. Tomorrow: We take a closer look at some of the teachers involved in the California Teachers Study.

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